One of the more pressing food problems facing the world today is the shortage of protein for human consumption. Many of the available proteins, such as those of plant and microbial origin, can be supplied in nutritional form but are generally unacceptable because of undesirable taste, flavor or texture. Most humans prefer the chewiness and mouthfeel characteristics of real meat. In order to make plants and microbial protein more palatable, food technologists have developed various methods to give the protein a textured or fibrous quality similar to real meat.
Prior art techniques for producing protein fibers have employed such diverse vegetable proteins as corn, cottonseed, peanut, rapeseed, safflower seed, and soybean protein. One of the most successful prior art techniques has been the wet spinning process developed by R. A. Boyer and disclosed in U.S. Pat. No. 2,682,466. In the Boyer process, protein fibers are prepared by forming an alkaline aqueous solution of the protein which is then extruded into an acid and salt coagulating bath to form fibers. One of the drawbacks in commercial practice of the Boyer process has been in the preparation of the material to be wet spun. It must be both bland in flavor and highly functional.
The functional properties of the protein encompass physicochemical properties such as dough-forming, water adsorption, fat-binding, emulsifying, foaming, film-forming, gelling, cohesiveness, adhesiveness, elasticity, etc. As used herein, the term "functional" means having sufficient collective characteristics to be capable of eventually forming acceptable wet-spun fibers. Generally, the functional properties of a protein will depend on the source, purity and degree of denaturation of the protein. Some proteins, such as safflower seed protein, require little purification and yet are functional as disclosed by L. F. Elmquist in U.S. Pat. No. 3,176,909. Other proteins, such as cottonseed, legumes, rapeseed, etc., however, contain undesirable carbohydrates and have "off" flavors such that only a highly purified form thereof will provide a satisfactory functional and bland starting material.
For example, when a soybean protein is used in the Boyer process, it is necessary to prepare a soy isolate which is a highly purified protein containing at least 90 percent protein. Preparation of the soy isolate is complex and time consuming and invariably results in the loss of functional protein. As a result, the use of soy isolate in the Boyer process is not totally satisfactory and substantially increases the cost of producing protein fibers.
Further difficulties are encountered in commercial practice of the Boyer process in the preparation of the spinning solutions. Conventional spinning solutions are usually prepared in large batches by dissolving the soy isolate in aqueous alkali and then ageing the solution. Depending upon the particular conditions of pH, solids content and temperature, the spinning solution will increase in viscosity until a spinnable viscosity is obtained. Under optimum conditions, the spinnable viscosity, i.e., 50,000 to 100,000 centipoise, is reached within 15 to 30 minutes and continues to increase thereafter to a maximum viscosity, after which it begins to decrease. As a result, the ageing process is time consuming and requires almost constant supervision to monitor viscosity.